Improvement in telephone-transmitters



C. A.-BANDALL.

- T'elephone-Transmitter.

No. 22I,355. Patented Nov. 4, !879.

4 Invenor:

X a/zarZJvZanaZaZL 1%wAM b day CHARLES A. RANDALL, OF'BROOKLYN, NEWYORK.

IMPROVEMENT IN TELEPHONE-TRANSMITTERS.

Spccification forning part of Letters Patent No. 221,:355, datedNovember 4, 1879; application filed April 7, 1879;

To all whom 't may concern:

Be it known that I, CHARLES A. RANDALL, of Brooklyn, in the County ot'Kings and State ot' New York, have invented certain new and useful Improvements in Acoustic Telegrapl y `or Telephonic Transmitters, of whichthe following` is a specification.

'This invention relates, especially, to that braneh of acoustictelegraphy which pertains to the transnission ot' articulate` speech;and it consists in an improved method of generating the electriccurrent, by means ot' which greater electro-motive force is obtained, sothat the lesser or more delicate air-vibrations will not fail to producetheir corresponding electric vibrations and transnit the same to thereceiving-instruinent, whe'eby more perfect articulation in louder andmore distinct tones is obtained at said receiving instrument.

It is not deened necessary to herein explain the principles involved inspeaki' g-telephones, as they are now generally well known. It is simplysufficientto say that in all tclephones capable of transmitting thesounds of articulate speech serious difficulties have been encountered,resulting from extreme sensitiveness, difficulties in adjustment, andwant of proper electro-notive power.

Aslight increase of power has been obtained in the later forms oftelephones-by the use of a battery and an induetion-coil, in the primarycircuit of which are located special contactmakers or tension-chahgers,but with this increase of power other difficulties are encountered,resulting from adjustments and inperfect articulation if the Voice istoo lond when speaking into the instruincnts, which ari ses probablyfrom the too-sensitive adjustment of the circuit-closer and from thereciprocal vibrations set up by the circuit-inaker, because of itsconstruction.

In telephonic transmission the first essential object is to accuratelyconvert the air-vibrations into electrcal impulses, and the second,which is quite as important, is to preserve the delicate air-vibrationsand obtain corresponding electrical vibrations of proper power to betransnitted to the receiving-instrunent.

The present invention is designed to eft'ect these objects in a moreperfect nanner than leretofore by ntilizig the well-known principle thata variable exposnre of a movable iron core in the prinary circuit ot' aninductioncoil perceptibl y affects and varies the intensity of thecurrent in the secondary coil, as familiarly demonstrated in theordinary galvanoelectric or shocking machines, by means of which shocksof varying intensity are obtained by shifting the core into and out ofthe coil.

To this end my invention consists, in combination with the diaphragm orvibrator, of a telephonic transmitter, an induction-coil having ainovable core, a oontact-inaker or tension-Changer located in theprima-y circnit, with mechanism wlereby it may be adjusted and themovable core'held against the diaphragm.

In the drawings, Figure 1 represents a longitudinal sectional View of myimproved teletelephonic transmitter. Fig. 2 represents a cross-sectionot' the transmitter. Fig. 3 represents a modification of thecircuit-naker.

The letter A indicates an induction -coil, constructed of two helices, ab, one within the other, as in an ordinary indnction-coil, except thatthe inner helix is constrncted ot' fine wire and the outer one of coarsewire. At the center of the inner heliX is located a movableiron core, B,which is, preferably, constrncted of a series of'soft-iron wires,secnred together in the same or a similar nanner to the soft-iron coreof an ordinary induction-coil. Said core is made somewhat shorter thanthe coil, in order that it may have a slight reciprocating motiontherein. i

To the lower end of the core is secured a ing rod secured to the casingD, and having an adjustable arm, F, provided with asetscrew, G, whichcarries a spiral spring, .H, having 'mounted on its free end abea-ringplate, h, of carbon or other poor conductor,

which is held in contact with the contact-point at the end ot` the rod Cby said spiral spring, and which may be made to bear against said pointwith a variable yielding pressure by means of the set-screw for thepurpose of adjustnent.

The lower end of the rod U is shouldered, as shown at c, the saidshoulder resting upon a Very flexible spring, I, which extendstransversely across the lower part of the casing D, and is adjustablySecured to screw-studs (Z on the same by means of check-nuts d'. Saidspring serves to take up the weight ot' the core and press said coreagainst the diaphragn.

The letter K represents the diaphragn, which is confined in theair-chanber L in the enlarged disk M, t'orning part of the casing D, andthe month-piece in any suitable man ner, in the present instace beingclanped between the disk and the mouth-piece.

The diaphragn is not nagnetic, and may be made of metal or any othersuitable material, and be held sccurely in place at the edges, or bymeans of atlexible washer or ring, N'.

The letter N represents a hollow oasing attached to the easing D toprotect the contactnaker from injury.

The prinary coil is connected with the battery-wire O and to the carbonhearing-surface on the upper end of the spiral spring by a wire, P, thenovable core being connected with the opposite pole ot' the battery by awire, R.

Thesecondary coil is connected with the linewire and the ground, asshown at S T.

The operation of my invention is as t'ollows: Upon speaking` into themouth-piece the diaphragm is put into ribration, noving the softironcore in the induction-coil back and t'orth in exact accordance with thesaid vibrations, which increases and decreases the contact at thecontact-maker, thereby changing the tension of the prinary eireuit. Atthe same time the vibrations of the iron core vary the intensity of thecurrent in the secondary coil, which, act-ing in conjunction with thevarying tension of the primary current over the prinary circuit,prodnces very m uch more marked,

distinct, and powerful induced currents or electric impulses in theseeondary circnit than can be obtained by the use of the contactmaker ortension-ehanger alone.

The special features of the contact-maker consist in so eonstructing itthat large or small contaet points may be used, as occasion requires,and in the adjustable spiral spring carrying one of the points, whichforms at once a yielding, yet comparatively firm, contact.

I do not claim, broadly, a spring forning or carrying one eleetrode ofthe circuit ot' a telephone and constantly pressing against the otherelectrode and diaphragm to maintain the required initial pressurebetween the electrodes and yicld to the movements of the diaphragn.

What I claim is- 1. In comhination with the diaphragn or vibrator of atelephonic transnitter, an induction-coil having a movable iron core,substantiall y as and for the purpose set forth.

2. In eonbi ation with the diaphragm or Vibrator ot' a teleplonietransnitter, an inluction-coil having a movable iron core, a battery,and a contact-maker or tc-nio-clanger, substantially as described.

3. The eombination, in a tcleplonie apparatus, of a diapbragm orvibrator, the novable iron core ot' an induction-coil, and acontact-maker or tension-changer having one or both ot' itscontact-surfaces attached to orsupported by a suitable elastic spiralspring, substantially as and for the purposes set forth.

4. In conbination with the movable iron core ot' the induction-coil, asuitable spring for supporting the weight of the core and pressing ort'orcing the same against the diaphragn, snbstantially as specified.

In testimoy that I claim the i'oregoing I have herennto set my hand inthe presence ol' the subserihing witnesses.

CHAS. A. RANDALL.

\\'itnesses:

JAMES L. NORRIS. .TAs. A. RUTIIERFORD.

